I know its not the most practical way about it but I'd like to look at making my own carbon fiber hood. If I were just to make a skin could I use the old hood as a mold? Would that slight difference in shape really cause that much effect? I'm just going to put 4 hood pins into the car and not use any of the hood attachments at all. I've read quite a bit into how to lay it up and plan on doing a few simple things first.

I just finished my daughter's Christmas present last month, a molded egg shaped chair built out of fiberglass clothe and epoxy. With out a doubt that was the biggest projects I ever did. Though not carbon fiber alot of the proceedures are the same. If I were to do it again I would have done several smaller projects and talked to alot of experienced people before starting it. Cost was double what I expected and took 10 times as long.

Then don't bag it. There is no harm in not bagging the carbon.
It is lighter if you can get the bagging to work and pull huge numbers, but it also becomes less fracture resistant. (Really, what is a little weight?)
We stopped bagging our boat hulls as leaving the resin in the lay-ups as the beatings these boats take are greatly aided by leaving the resin in and making them more impurvious to large bumps and slams on waves. Also good on certain parts of funny car bodies.
If you want some back yard DIY lightening, grab a sheet of heavy wax paper, then spray your mold release on the wax side and get ready. Then after everything is wet and saturated, lay the wax paper on and grab a squeegie. Squeegie out the extra resin and air to the outside of the part. Then after everything is activated, take the way paper off and have a semi-glossy backside to your part. Because we have found that pulling vacuum is most helpful in getting the air out first, then - second - getting the extra resin out. The wax paper trick does both.
But with the vacuum stuff, it can be tricky and costly. Why not make it really strong for really cheap? That is why we want carbon, right?

If your going to make a part from an overlay of the original . A cheap diy approach could be had with a little peel ply and some sand bags .Once you saturate the carbon fiber with your epoxy resin while being mindful of weave distortion , lay the peel ply over your part and cover it all with a good layer of sand up until the point where the equal weight distribution holds the impregnated fabric down . Once its all dry you can pull off the peel ply and the sand will lift with it . That will leave the typical appearance of having been vacuum bagged and from a hobbyist standpoint , no one will know .

BP, is this just for appearance or for some race series? Reason I ask is, at higher speeds, a simple slab hood can buckle up like a newspaper in the wind, then when the car slows down, the excellent springing of the fiberglas will restore the shape and you're looking at trying to diagnose weird aerodynamics with no clues. Hot Rod magazine some years back ran photos of cars 'in the eyes' at drag strips across the country, and there were severely crumpled-up fiberglas parts showing at speeds as low as 120 mph. Incorporating reinforcement beams in fiberglas complicates your project a little but has benefits if you plan to go 'fast'. Sometimes, the reinforcing beams are urethane-foam-filled after hardening. As to supplies, Aircraft Spruce (home-built aircraft) sells fiberglas and carbon-fiber cloth, resins and so forth, quite resonably.

The best mold release system/agent is PVA, sprayed on properly, its water soluble, low cost, easily removed or reapplied for each single use, there are other considerations, but it works well . Not sure its been mentioned, most of the skill set for doing fiberglass, is the same for CF, to achieve all of CF useful benefits, techniques like bagging as needed, but not required. And most of one's effort is usually spent in making a quality mold, which kinda sucks for a one off. Its also a lot easier if one is willing to have a finished painted CF item vs needing near perfect fabric lay for cosmetics, which also provides UV protection..